1. Field of the Invention
The invention relates to the production of poultry, and more particularly to increasing the efficiency of poultry production by acting on hormonal functions of the birds.
2. Description of the Prior Art
The intense genetic selection of turkeys, chickens and other poultry has achieved dramatic increases in body size and growth rates. However, it is well known that genetic selection has adversely affected the efficiency of poultry production by causing alarmingly low average hatchability rates for the eggs, as low as about 70% for many strains of domestic turkeys.
Current efforts to optimize the hatchability of poultry eggs have centered primarily on optimizing the controlled enviromental conditions (e.g. temperature, humidity and gas concentrations) for egg incubation. Other steps, including the injection of antibiotics at different stages of incubation, have been used to control disease.
Looking at domestic turkeys as an example, it is known that over 90% of the embryos of domestic turkeys are alive at or near days 24-25 of incubation, indicating that a very large and significant number of the embryos that do not hatch die late in incubation.
The literature suggests several factors, perhaps interrelated, that may contribute to late embryonic mortality. First, it is known that the eggs breathe totally by gas diffusion through the eggshell (so that the embryo is unable to adjust its gas diffusion rate to coincide with its metabolic rate via increased muscular contraction as mammals, fishes or adult birds do). Therefore, the functional gas conductance properties of the eggshell must be precisely engineered by the hen laying the egg to supply vital gases to an increasing tissue mass. In wild species this delicate balance exists. However, the genetic selection of domestic poultry has caused a dissynchronous relationship between functional eggshell properties and the O.sub.2 and CO.sub.2 and water vapor requirements of the embryos.
A second observation has been that thyroid hormones play an important physiological role in the successful hatching of domestic poultry. Experimental data have indicated that plasma thyroxine (T.sub.4) concentrations appear to be significantly greater at days 26 and 27 of incubation in high hatchability groups of domestic turkey eggs. The high hatchability groups also show significantly higher oxygen consumption, indicating a higher metabolism.
While the above and other phenomena have been suggested by experimental data, prior to this invention there have been no modifications to time honored incubation processes to address the problem of late embryonic mortality.
It is well known that other factors, including feed conversion rates and mature bird weight, have a significant bearing on the overall efficiency of poultry production. The poultry industry has a continuing need for process developments that will optimize these key factors.